Abstract: To study the deformation characteristics and environmental impact of semi-covered deep foundation pit adjacent to existing buildings, taking the foundation pit engineering in soft soil area of Nanjing Metro Line 5 Shanxi Road Station as example, and adopting foundation form and support form as variables, 8 groups of numerical simulation working conditions are designed and analysed. Research results show that existing buildings cause eccentric loads on one side of the foundation pit, leading to the overall movement of diaphragm wall lateral curve into the pit. The rigid connection between cover plate and diaphragm wall makes the wall top warp, and the embedment of diaphragm walls into rock stratum limits the lateral movement of the bottom and changes the shape of diaphragm wall bottom lateral curve. The land subsidence curve outside the pit is greatly influenced by the form of building and its foundation, and has little relation with cover plate and depth of diaphragm walls. The foundation pit excavation mainly affects soil settlement in the triangular area within 2 times of depth behind the wall, and the existing building basement and pile foundation can effectively control the soil settlement size and scope on the side of the building close to foundation pit.